Emissions of nitrogen oxides (NOx) contribute to adverse health and causes formation of ozone, acid rain, and particulates. One of the most efficient technologies commercially utilized to reduce NOx emissions is selective catalytic reduction (SCR). This technology utilizes a catalyst and reagent to reduce NOx to nitrogen (N2) and water (H2O).
Traditionally ammonia, as a reagent, is injected and distributed across a ductwork through a system of round pipes (lances) equipped with injection holes or injection nozzles. A long distance between the injection point and the SCR catalyst must be assured to allow for acceptable turbulent mixing of the reagent and flue gas. Shortening the distance between the injection point and the catalyst is desirable. In new construction, a long distance is often unavailable due to a limited footprint for the ductwork. In a retrofit application, a long distance may require cost prohibitive modifications to the existing system. To increase the mixing efficiency and reduce the required mixing distance (and the corresponding capital expenses) many SCR installation are equipped with static mixers. Static mixers typically have elaborate designs, high fabrication and installation costs, and they cause a significant pressure drop. The conventional static mixers are typically installed between the ammonia injection pipes and the SCR catalyst, however local deflectors attached to the injection nozzles or turbulence enhancers installed between the injection pipes have also been utilized.
A need exists to more effectively provide turbulent mixing between fluids such as ammonia and flue gas in a shorter distance and preferably without the need for a static mixer.